On Nov 22, 9:14, Eric J. Korpela wrote: appropriate net. to. Mbps It's done by a protocol involving exchange of patterns of link pulses when the link is first established. Full duplex and 100Mb capability are offered (separately, and there are a few devices that support full duplex 10Mb although it's not part of the standard) by one side of the link; if there's no approriate response from the other end, the link remains at 10Mb half-duplex (ie, normal 10baseT). Well, strictly speaking, such dual-speed hubs are actually 2-segment repeaters that are very like simple switches (or a bridge). They buffer the data between the fast and slow segments, and on the cheaper ones that can reduce the performance significantly. had Unless you only have a few, you've been lucky. I look after around a dozen serious switches and about 3 dozen hubs, and in the last four years we've had around half a dozen failures. Of course, one or two have been simple, like dead fans causing a hub to overheat, and we've had at least three instances of a single port failing. That's a lot fewer failures than we have on PCs, but then we have a lot more PCs! This is comparable to the rates seen by my colleagues across campus, incidentally. You should also bear in mind that ethernet is amazingly tolerant, and there can be intermittent failures, dropouts, links that fall back to half duplex etc which you won't notice unless your management system is fairly good. There is, at least in the UK. I don't know if it would apply in the States, since you use two wires (one pair) for the phones and we use three (a pair and a half, but we normally also connect the fourth wire between nodes). Anyway, 10baseT and 100baseT use pins 1,2,3, and 6; the phones use 3,4,5, and 6; ISDN uses 3,4, 5 and 6 for data and carries power on the other two pairs. You normally plug a little white box containing a phone socket and PBX termination into the RJ45 wall socket. ISDN uses RJ45 plugs so nothing extra is required (unless it's a long run or multiple sockets and you need a terminator on the end). You can get little doublers that have one RJ45 plug on a short lead connected to a small box with two RJ45 sockets, wired in such a way that you can plug a 10[0]baseT into one side and a phone line into the other; connect the plug to a patch panel, and reverse the process at the other end (wall socket) to separate the signals again. They're meant for places where there's not enough "horizontal" wiring (the under-floor/overhead/behind-walls runs from patch panel/wiring closet to wall socket). You can also get ones that double up 2 x 10[0]baseT onto one cable, using all four pairs instead of two. The phone won't be hurt by the net devices, but it's possible the net devices might be surprised by phone/ISDN voltages. However, as far as I know, we've never had a mishap (touch wood). It's called "structured wiring", and that's what patch panels are for :-) All our ethernet, serial, ISDN, and POTS signals are carried on the same wiring and patch panels (except for the fibre, of course). We have about 800 RJ45 wall and floor sockets, not counting the patch panels, in our building for exactly that reason. I have about a couple of dozen at home, but I also have quite a few DB25s, BNCs, and phone sockets :-) -- Pete Peter Turnbull Network Manager Dept. of Computer Science University of York